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If you take octave transpositions as requiring negligible thought, then the only extra clefs you need to learn for score-reading orchestral music are: Soprano - A, Tenor - Bb, and Alto - violas (D in Baroque and Brahms, maybe). Bass clef will do for E and Eb leaving (horns in)F/cor anglais which is probably worth just practising as transposition. The idea is that you learn the clefs not work them out on the fly.